The Office of Public Safety of the municipality shall have the power to modify any of the provisions of the National Fire Prevention Code, 1960 Edition, adopted as part of this chapter, upon application, in writing, by the owner or lessee or his duly licensed agent, when there are practical difficulties in the way of carrying out the strict letter of such provisions, provided that the spirit of such provisions shall be observed, public safety secured and substantial justice done. The particulars of such modification, when granted or allowed, and the decision of the Office of Public Safety thereon shall be entered upon the records of the Fire Department, and a signed copy shall be furnished the applicant.